In the interview he explains that they did not go through a proper YC batch because "the timing didn't really work out". They had been through the process before and he had got to know pg well. Hope that helps!

I didn't think they were in one of the batches (haven't seen the usual YC'whatever badging on any of their posts' titles here). Their job post from a while back (http://news.ycombinator.com/item?id=3099362) does list YC as an investor, though.

Edit: Patrick's previous startup, Auctomatic, was in YC W'07 I think. Maybe that has something to do with it.

I'm glad I asked, then. I'm confident someone with direct knowledge will come in and provide more information. :)

Listen at 13.40, he mentions that although first funding came from YC they didn't go through a YC batch - Patrick had previously been a YC member with another startup: "Auctomatic".

Harj and I did Auctomatic in Winter 07. We merged with Patrick just after YC. Harj is now a YC Partner. I did YC for the second time this summer with Tagstand.com.

I mention the merger here in a series of Viewpoints for the BBC: http://news.bbc.co.uk/2/hi/business/6701815.stm

Also, the outcome of Auctomatic: http://news.bbc.co.uk/2/hi/business/7315598.stm